Process for stabilizing or deactivating sludges, precipitates, and residues occurring or used in the manufacture of tetraalkyl leads



Patented Sept. 10, 1946 PROCESS FOR STABILIZIN G OR DEACTIVAT- ENG SLUDGES, PRECIFITATES, AND RESI- DUES OCCURRING OR USED IN THE MAN UFACTURE OF TETRAALKYL LEADS Adrian L. Linch, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware N0 Drawing. Application September 16, 1942,

' Serial No. 458,580

4 Claims. (01. 260-437) This invention relates to a process for stabilizing or deactivating sludges, precipitates and residues occurring or used in the manufacture of tretraalkyl leads, and which normally tend to promote decomposition and ignition of the tetraalkyl leads that may be contained therein.

It is known that alkyl metal compounds in general are quit unstable and decompose readily, particularly in the presence of air or oxygen. It has also been found that these alkyl metal compounds are particularly unstable when adsorbed on materials which present a large surface area per unit volume such as silica gel, clays, alumina, earths, asbestos, charcoal, and materials of similar structure which materials appear to exert a catalytic efiect in the decomposition of these alkyl metal compounds. Even tetraalkyl leads such as tetraethyl lead which is known to be somewhat more stable than some of the other alkyl metal compounds decomposes and often ignites in the presence of oxygen when small amounts are adsorbed on materials that ofier extended surface areas, particularly when the masses containing the tetraethyl lead are exposed to temperatures somewhat higher than normal atmospheric temperatures. The tendency to oxidize and ignite of course varies with the substance With which the alkyl metal compound is incorporated, some materials apparently exerting a greater catalytic efiect than others in promoting ignition of the alkyl lead compounds.

In the manufacture of tetraalkyl leads, such as tetraethyl lead, tetramethyl lead and the mixed ethyl-methyl lead compounds, sludges are formed from which it is difficult and, from a practical standpoint, impossible to entirely free from the alkyl lead compounds during the normal steam distillations or decantation operations. There is, therefore, carried through the process very finely divided lead and impurities such as bismuth con pounds which, although present in very small amounts, finally are deposited as sludges in the pipes and tanks and other processing equipment and these sludges which contain tetraethyl lead adsorbed therein when exposed to oxygen or air often ignite, thus presenting serious ignition and explosion hazards in the process.

Methods have been advanced for the removal of practically all the sludge forming materials from the tetraethyl lead after its distillation, such as by controlled blowing with air or oxygen with agitation, preferably under a layer of water, followed by separation of the precipitated sludge. as more particularly described in copending application Ser. No. 393,680. However, even in these cases the sludges which are deposited by the action of the oxidizing agent and which invariably contain tetra-ethyl lead, tend to ignite when exposed to air thus presenting serious ignition hazards, making it desirable that even these sludges should be deactivated during their formation or afterwards to permit of their removal and disposal in a safe manner.

It is therefore an object of this invention to provide a process for stabilizing sludges, precipitates and residues occurring in the manufac ture of tetraalkyl lead compounds whereby the ignition hazard presented by the lead alkyl compounds in contact with such catalytic surfaces is reduced or completely overcome.

It is a still further object of the invention to render inactive materials which tend to exert a catalytic effect in the decomposition of tetraalkyl leads in the presence of air thus permitting the safe use of such materials as filter aids in the manufacture of tetraalkyl lead.

I have found that sludges, precipitates and residues occurring or involved in the production of tetraalkyl leads which offer large surface areas per unit volume and which normally tend to exert catalytic effect and cause decomposition and ignition of the tetraallryl lead which may be contained therein can be rendered inactive conveniently and economically by washing or otherwise treating them with solutions or dispersions of trivalent organic nitrogen compounds. These stabilizing or deactivating agents appear to be preferentially absorbed by the active materials, which materials retain their capacity to absorb the tetralkyl lead although they no longer have the property of inducing ignition of the tetraalkyl lead absorbed therein.

By the terms sludges, precipitates and residues We include those filter aids which may be employed in the production of the tetraalkyl leads and which offer a large surface area per unit volume and are known to accelerate decomposition of the tetraalkyl leads on exposure to air or oxygen such as clays, silica, earths, charcoal, etc. These filter aids ar rendered. inactive by trating them with trivalent organic nitrogen compounds either before or after they are employed in the process. The effectiveness of the trivalent organic nitrogen compounds in the deactivation of these active materials is not materially reduced by washing the deactivated materials with water or other solvents or by drying them down prior to use.

The trivalent organic nitrogen compounds that may be employed for this purpos 'may be primary, secondary, or tertiary, aliphatic or aromatic amines, or the may be trivalent nitrogen compounds in which the nitrogen forms part of a heterocyclic ring. Those which have been found to be useful vary widely in chemical com-- position and in molecular weight. The only limitations upon this class of compounds, insofar as I have been able to determine, is that if they are straight alkyl amines or unsubstituted ary1- amines they should contain at least seven carbon atoms in at least one alkyl or aryl group and in both the aliphatic and aromatic series they should not contain a free sulfonic acid group. The sulfonic acid group as such appears to render these amines sludges and residues although substituted sulfonic acid groups may be present in the molecule without rendering them inoperative as deactivating agents. Aniline itself, which is the simplest member of the aromatic series, is very weak in its deactivating power and can be used only with the less active type of residues or other materials which tend to exert the catalytic effect in a more mild degree. The simple substituted anilines such as para amino phenol, para nitro aniline, etc, s

have been found to deactivate the most active types of residues. active materials of the type mentioned does not appear to depend upon whether the materials are soluble or insoluble in water or other solvents from which the may be applied to these residues.

As illustrative of the types of trivalent nitrogen compounds that may be employed are those having the general formula wherein R (1) An aryl group substituted by one or more of the following: -OH, -COOH, COO metal, NO2, CHO, 0 alkyl, --0 alkyl OH, NH2, arylNHz, --Saryl, alkyl (more than 4 carbon atoms), phthaloyl;

incapable of deactivating the active The property of deactivating 4 (2) An alkyl group substituted by one or more of the groups, -OH, COOH, COO metal; (3) A long chain alkyl (more than 8 carbon atoms) (4) -(||JNHCNH2 EN EN (or nitrogen substituted derivatives), (5)

in which R3 is an aryl grou substituted by -OII;

(6) -SO2-R4 in which R4 is an aryl group substituted by NH2 or by an alkyl group or Where R4 is a long chain alkyl (more than 8 carbon atoms) R1=II, alkyl, aryl, substituted alkyl or substituted aryl; (R and R1 together may be =Caryl substituted by -OH) R2:=H,' alkyl, aryl, substituted alkyl, substituted aryl or heterocyclic.

The trivalent organic nitrogen deactivators are preferably used as aqueous solutions which contain the deactivating agent in an amount equivalent to approximately one-third of the dry weight of the material to be stabilized. The amount of deactivator employed may, of course, be varied over a Wide range with equally good results. By employing the stabilizer in an amount ranging from 0.05% to more than 100% of the dry weight of the active material, satisfactory results have been obtained. The stabilizing efiect may be obtained in some cases by using even smaller amounts of the deactivating agent, although a surficient amount should always be used to insure complete deactivation of the active material. The use of excessively large quantities over that actually required to deactivate the active materials merely contributes unnecessarily to the cost of the process and serves no useful purpose.

The deactivating agent is preferably employed in a solution of a concentration of from 1 to 5% although lower or higher concentrations may be used. It is, of course, advantageous to employ a sufilcient amount of solution to insure complete contact of all the material to be deactivated. To prevent the use of unnecessary large amounts of the deactivating agent, it will usually be found desirable to use a relatively large volume of solution of a concentration of less than 5%. Where there is an advantage of employing a lesser volume of solution, the concentration may, of course, be increased.

An important use of the present invention in the commercial manufacture of tetraethyl lead is to deactivate the sludges which are precipitated and removed from the crude tetraethyl lead in the purification step. A method of precipitatting and removing these sludges by treating the crude tetraethyl lead with oxidizing agents such as with air or oxygen is more particularly disclosed in copending application Ser. No. 393,680. The precipitated sludges from this process collect in the aqueous layer from which the purified tetraethyl lead is separated by decantation. Although dispersed in the water layer the sludge retains sufiicient tetraalkyl lead absorbed therein to ignite on contact With oxygen or air, particularly at slight ly elevated temperatures. In order to permit the safe handling and disposition of these sludges, it has been found desirable to deactivate them before they are removed from the system. This can be done conveniently by adding a quantity of one of the deactivating agents to the aqueous sludge dispersion and then agitating the mass to assure complete contact of all the sludge with the deactivating material, or an aqueous solution of the deactivating agent may be used to cover the tetraalkyl lead during the accelerated sludge precipitation treatment so that the sludge is deactivated as fast as it is formed.

The deactivating material may be employed in an aqueous solution or suspension or in other solvents.

Where the sludges or precipitates settle out in the pipe lines or other processing equipment during the manufacture or purification of the tetra alkyl leads, they may be deactivated, to insure safety in their removal or during repair of the equipment, by pumping a solution of one of the deactivating materials through the apparatus for a sufiicient period of time to insure complete contact with all the sludge to be deactivated, which is usually accomplished in from 15 to 30 minutes.

Thefilter aids may be washed with a solution of the deactivating agent prior to their use in the process. They may be employed either before or after drying, for it has been found that they do not again become active even after being dried. or by being washed by the solutions that are filtered therethrough.

' A further use of the invention is found in the storage of crude tetraalkyl lead before it is desludged by accelerated sludge precipitation. An aqueous solution of one of the deactivators disclosed may be used to cover the crude tetraalkyl lead. Any sludge which precipitates at the surface of the lead alkyl on standing is stabilized by contact with the aqueous layer. If desired, all of the precipitated sludge may be brought into the aqueous layer by suitable a itation since the stabilized sludge particles readily disperse in the water layer. In this way the sludge may be deactivated as soon as it is formed.

The following examples are given to illustrate the invention. The parts used are by weight.

Example 1 Approximately 10,000 parts of crude tetraethyl lead were processed in a washer to precipitate the sludge-forming impurities by the method described in the co-pending application, Ser. No.

393.680. The precipitated sludge, which by laboratory analysis of a small sample had been calculated to weigh 12 parts, was collected in 1,000 parts of water. The purified tetraethyl lead was then decanted from the water layer. Approximately parts of p-amino phenol were added to the aqueous phase producing a solution of about 1% p-amino phenol. The mixture was agitated for 15 minutes and filtered.

A small portion of the filter cake was then tested for ignition activity by placing it on a' filter paper, wetting the cake with a small quantity of tetraethyl lead and heating on a steam bath. No signs of ignition or of charring of the filter paper were noted even after 24 hours on the steam bath.

A sample of the same sludge which was taken before the p-amino phenol was added to the water layer was tested for activity as outlined above. Ignition occurred shortly after the initial sample was placed on the steam bath.

In regular plant application of this method of sludge deactivation, it may not always be convenient to run a laboratory analysis in order to determine the amount of sludge to be expected, and such a procedure is not necessary. We have found that under usual conditions the quantity of sludge formed per 1,000 parts of tetraethyl lead seldom exceeds 2 parts, and this figure may be used as a basis for the calculation of the quantity of deactivator needed. Thus, if we add 0.6 part (30% of the dry sludge weight) of deactivating agent to the water layer per 1,000 parts of tetraethyl lead, sufficient deactivator is present to meet any conditions which we have met. Of course, tetra-ethyl lead manufactured in various plants may vary in sludging capacity depending on quality of raw materials, but in any one plant the quantity is relatively constant, and a definite amount of deactivator per unit Weight of tetraethyl lead may be easily set up as adequate in all cases.

Example 2 Approximately 2,000 parts of crude tetraethyl lead were placed in a suitable container provided with means for agitating its contents. About 200 parts of water were added, and the sludge was precipitated and collected in the water layer as disclosed in the previously mentioned application No. 393,680.

After the precipitation treatment was com plete, five parts of para-phenylene diamine were added, and the contents of the container 'were agitated for about 15 minutes. The tetraethyl lead and the aqueous layer were then filtered together, and the clear tetraethyl lead was decanted from the water layer after filtration was complete. A sample of the sludge retained on the filter was tested for ignition activity as previously described, and was found to be inactive. Sludge obtained using the same crude tetraethyl lead and the same process, except that no paraphenylene diamine was added. ignited the tetraethyl lead which it retained when placed on the steam bath.

It is, of course, understood that other trivalent organic nitrogen compounds may be employed in this example in place of the para-phenylene diamine. The quantities and concentrations employed in this example are not to be construed as limits to the invention, for they may be varied widely without altering the results obtained.

While in the preceding examples We have used stabilizing agents which are soluble in neutral vents.

aqueous solutions, deactivating agents that are insoluble in neutral aqueous solutions may be effectively applied from suitable solutions, such as dilute sodium hydroxide, or from organic sol- We have found that dispersions, suspensions or solutions of the deactivating agent in solvents other than water may be effectively used. Where water is used as the solvent or dispersing medium, the method of applying the deactivator to precipitated tetraalkyl lead sludges is effective when applied as set forth in Examples 1 or 2. However, when solvents other than water are used, the aqueous layer containing the sludge may be filtered off, and the filter cake then agitated with the solution containing the deactivating agent for a period of from 15 to 30 minutes in a suitable receptacle, or the solvent solution may be added directly to the aqueous sludge suspension. Results obtained on agitating 10 parts of an active sludge with 50 parts of a solution of representative trivalent organic nitrogen compounds in various solvents are listed in the table below.

salicylal sorbityl amine were then added to the water layer, and the sludge was precipitated and Steam bath stability oncen-g Compound tration Solvent Initial After 21 hrs. After 72 hrs.

Per cent Para phenylene diamine Water No decomposi- No decomposi- No decomposition. tron. tion. Ortho phenylene diamine Do. Guanyl guanidine sulfate Do. 1, 4 di (para tuloido) anthraquinona- Do. Anthranilic acid 50% ethanol Do. Para amino phenol Water. Do. Salicylal sorbityl amine (1 Do. Di (betaehydroxyethyl) aniline Do. Meta-amino benzaldehyde Do. Dimethyl cetylamine Do. Para dodecylaniline. Do. Stearylamine. i Do. Meta nitro aniline. Do. Salioylal propylene d1am1nc condensation product Do; 2-hydroxy-3-naphthanilide Do. Suliapyridinc Do. N-di-n-butyl para amyl benzene sulfonan11de D0. N-isobutyl para amyl benzene sulfonamidm Do. 1, 4-di(p-tolylamino) anthraquinone Do. Methyl glucamine Do. 3 (4 hydroxyphenyl) amino carbazo1e Do. Para amino phenyl acetic acid Do. Para phenetidine D0. Para (hydroxy ethoxy aniline Do. Dodecyl sulfonyl mono ethanol amide Do. lndole D0. N o deactivator (control) As previously stated the invention may be employed to stabilize active filter aids which are to be used in tetraalkyllead filtration. These materials may be washed in a solution of one of the deactivators and rendered suitable for tetraalky] lead. filtration. The following filter aids as well as a number of other materials of similar structure were wet with tetraethyl lead and placed on a steam bath as described in Example 1 above. All were found to initiate the ignition of tetraethyl lead. Ten parts of each of these materials were then agitated for several hours with 50 parts of the solution of various trivalent organic nitrogen compounds of the concentrations given in Table 2. Where no solvent is specified, water is used. After the agitation period, I

the solutions were filtered and portions of the filter cakes were wet with tetraethyl lead and placed on a steam bath. Results of the tests are given below:

Material Nash solution Steam bath test Filter aid (clay) Yellow lead oxide (N. F.

Bismuth subnitrate.

Bismuth oxide (from hydrolysis ofBi(NO3)2). Do

Ferric oxide (anh) Do Activated Al1unina Do-.

Decolorizing charcoaL Do None 5% p-amino phenoL- one 1% p-phenetidinc in ethanol.

None

2% M-nitro aniline in ethanol.

None

5% anthranilic acid in 50% ethanol.

None

5% rnethyl gluca mine.

None 1% salicylal scrhityl amine.

None .i 2% dimcthyl cctylamine in ethanol. None 5% guanyl guanidine sulfate.

Ignited.

No decomposition. Ignited.

No decomposition.

Ignited.

No decomposition.

Ignited. No decomposition.

Ignited.

No decomposition.

nited. No decomp sition.

Ignited. No decomposition.

Ignited. No decomposition.

Example 3 removed from the tetraethyl lead by the method disclosed in the co-pending application Ser. No. 393,680. After this operation was complete, the tetraethyl lead was removed by decantation, and the aqueous layer containing the sludge was filtered. A portion of the filter cake was then tested on the steam bath as described in Example 1. No decomposition or ignition of the tetraethyl lead was noted.

Example 4 As previously stated, sludges found in tetraethyl lead are also found in other lead alkyls which are manufactured from commercial lead. An example of these alkyl are the mixed tetramethyl-ethyl compounds of lead, formed when a mixture of methyl chloride and ethyl chloride are reacted with lead sodium alloy. All examples in which tetraethyl lead is specified are equally workable with these mixed lead alkyls.

Approximately 8,000 parts of crude mixed tetramethyl-ethyl lead compounds (tetramethyl lead, trimethyl ethyl lead, dimethyl diethyl lead, methyl triethyl lead and tetraethyl lead) were placed in a suitable tank or washer, and 2,000 parts of water containing 20 parts of sodium hydroxide and 20 parts of 3 (4-hydroxy phenyl) amino carbazole were added. The contents of the tank were aerated and agitated for two hours as disclosed in the copending application Ser. No. 393,680. Aftera settlin period of a few minutes, the clear mixed lead alkyls were decanted from the aqueous layer and the aqueous mixture was filtered. A portion of the filter cake was tested on the steam bath as described in Example 1, except that the filter cake (sludge) was wet with mixed lead a kyl compounds rather than with tetraethyl lead. No decomposition or ignition of the lead alkyls was noted. A similar experiment Was carried out in which no stabilizing agent was placed in the water layer. This sludge ignited the mixed alkyls when the steam bath stability test was made. I

In testin th activity of the sludges before or after treatment with the deactivating agents, it will be noted that tetraethyl or other alkyl lead was added to the residues. This was to make sure there was sufiicient tetraalkyl lead present to ignite under the conditions employed, if the sludge was not fully inactivated, for in some instances, it is possible that the amount of alkyl lead may be reduced to such a small amount that ignition might not be noted. While the elimination of the alkyl lead from the residues to such an extent does not ordinarily take place,- the tests were made under conditions favoring ignition provided the sludge or filter aid was active.

This invention makes possible the deactivation of the ignitable sludges and residues occurring in the manufacture of tetraalkyl lead compounds and is of particular value in eliminating fire and explosion hazards involved in the removal and disposal of such sludges from the process and in overcoming the potential fire hazard arising from the collection of such sludges and precipitates which accumulate in various places in the processing equipment and which when exposed to air often ignite with considerable damage. The invention also permits the use of filter aid which, unless rendered inactive, tend to cause ignition of any absorbed tetraethyl lead when they are exposed to the air. Any other absorbent materials which for any reason may become saturated with tetraethyl lead in or about the plant in which it is being manufactured may be rendered inactive by washing or otherwise treating with stabilizers of the type described so that potential fire hazard may be removed as far as possible. Lagging on pipe which due to leaks may become saturated with tetraethyl lead and which have been known to cause its ignition can be inactivated by treating such lagging with the deactivating agents.

I claim:

1. The process for inhibiting the spontaneous ignition of tetraalkyl lead compounds adsorbed on sludges which are precipitated from crude tetraalkyl lead compounds and which sludges normally tend to cause spontaneous ignition of the tetraalkyl lead compounds adsorbed thereon when exposed to oxygen, which comprises washing such sludges with p-amino phenol in an aqueous carrying medium in an amount sufficient to provide at least 0.05% of the p-amino phenol based on the dry weight of the sludges.

2. The process for inhibiting the spontaneous ignition of tetraethyl lead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises washing such sludges with p-amino phenol in an aqueou carrying medium in an amount sufiicient to provide at least 0.05 of the p-amino phenol based on the dry weight of the sludges.

3. The process for inhibiting the spontaneous ignition of tetraethyllead adsorbed on sludges which are precipitated from crude tetraethyl lead and which sludges normally tend to cause spontaneous ignition of the tetraethyl lead adsorbed thereon when exposed to oxygen, which comprises washing such sludges with m-nitro aniline in an aqueous carrying medium in an amount sufiicient to provide at least 0.05% of the m-nitro aniline based on the dry weight of the sludges.

4. The process for inhibiting the spontaneous ignition of tetraalkyl lead compounds adsorbed on sludges which are precipitated from crude tetraalkyl lead compounds and which sludges normally tend to cause spontaneous ignition of the tetraalkyl lead compounds adsorbed thereon when exposed to oxygen, which comprises washing such sludges with an aromatic amine in an aqueous medium such aromatic amine being a member of the group consisting of p-aminophenol, m-nitro aniline, para nitro aniline, paraphenylene diamine, ortho phenylene diamine, 1,4 di(para toluido) anthraquinone, anthranilic acid, di(beta hydroxyethyl) aniline, meta amino benzaldehyde, para dodecylaniline, 1,4-di(ptolylamino) -anthraquinone, para amino phenyl acetic acid, para phenetidine and para(hydroxy ethoxy) aniline.

ADRIAN L. LINCH. 

